PC World 2001 April/PCWorld_2001-04_cd.bin/Software/TemaCD/webclean/!!!python!!!/BeOpen-Python-2.0.exe/SAFE.TCL

Text File | 1999-08-18 | 26.9 KB | 923 lines

# safe.tcl --
#
# This file provide a safe loading/sourcing mechanism for safe interpreters.
# It implements a virtual path mecanism to hide the real pathnames from the
# slave. It runs in a master interpreter and sets up data structure and
# aliases that will be invoked when used from a slave interpreter.
#
# See the safe.n man page for details.
#
# Copyright (c) 1996-1997 Sun Microsystems, Inc.
#
# See the file "license.terms" for information on usage and redistribution
# of this file, and for a DISCLAIMER OF ALL WARRANTIES.
#
# RCS: @(#) $Id: safe.tcl,v 1.6 1999/08/19 02:59:40 hobbs Exp $

#
# The implementation is based on namespaces. These naming conventions
# are followed:
# Private procs starts with uppercase.
# Public  procs are exported and starts with lowercase
#

# Needed utilities package
package require opt 0.4.1;

# Create the safe namespace
namespace eval ::safe {

    # Exported API:
    namespace export interpCreate interpInit interpConfigure interpDelete \
        interpAddToAccessPath interpFindInAccessPath setLogCmd

    ####
    #
    # Setup the arguments parsing
    #
    ####

    # Share the descriptions
    set temp [::tcl::OptKeyRegister {
    {-accessPath -list {} "access path for the slave"}
    {-noStatics "prevent loading of statically linked pkgs"}
    {-statics true "loading of statically linked pkgs"}
    {-nestedLoadOk "allow nested loading"}
    {-nested false "nested loading"}
    {-deleteHook -script {} "delete hook"}
    }]

    # create case (slave is optional)
    ::tcl::OptKeyRegister {
    {?slave? -name {} "name of the slave (optional)"}
    } ::safe::interpCreate
    # adding the flags sub programs to the command program
    # (relying on Opt's internal implementation details)
    lappend ::tcl::OptDesc(::safe::interpCreate) $::tcl::OptDesc($temp)

    # init and configure (slave is needed)
    ::tcl::OptKeyRegister {
    {slave -name {} "name of the slave"}
    } ::safe::interpIC
    # adding the flags sub programs to the command program
    # (relying on Opt's internal implementation details)
    lappend ::tcl::OptDesc(::safe::interpIC) $::tcl::OptDesc($temp)
    # temp not needed anymore
    ::tcl::OptKeyDelete $temp


    # Helper function to resolve the dual way of specifying staticsok
    # (either by -noStatics or -statics 0)
    proc InterpStatics {} {
    foreach v {Args statics noStatics} {
        upvar $v $v
    }
    set flag [::tcl::OptProcArgGiven -noStatics];
    if {$flag && ($noStatics == $statics)
              && ([::tcl::OptProcArgGiven -statics])} {
        return -code error\
            "conflicting values given for -statics and -noStatics"
    }
    if {$flag} {
        return [expr {!$noStatics}]
    } else {
        return $statics
    }
    }

    # Helper function to resolve the dual way of specifying nested loading
    # (either by -nestedLoadOk or -nested 1)
    proc InterpNested {} {
    foreach v {Args nested nestedLoadOk} {
        upvar $v $v
    }
    set flag [::tcl::OptProcArgGiven -nestedLoadOk];
    # note that the test here is the opposite of the "InterpStatics"
    # one (it is not -noNested... because of the wanted default value)
    if {$flag && ($nestedLoadOk != $nested)
              && ([::tcl::OptProcArgGiven -nested])} {
        return -code error\
            "conflicting values given for -nested and -nestedLoadOk"
    }
    if {$flag} {
        # another difference with "InterpStatics"
        return $nestedLoadOk
    } else {
        return $nested
    }
    }

    ####
    #
    #  API entry points that needs argument parsing :
    #
    ####


    # Interface/entry point function and front end for "Create"
    proc interpCreate {args} {
    set Args [::tcl::OptKeyParse ::safe::interpCreate $args]
    InterpCreate $slave $accessPath \
        [InterpStatics] [InterpNested] $deleteHook
    }

    proc interpInit {args} {
    set Args [::tcl::OptKeyParse ::safe::interpIC $args]
    if {![::interp exists $slave]} {
        return -code error "\"$slave\" is not an interpreter"
    }
    InterpInit $slave $accessPath \
        [InterpStatics] [InterpNested] $deleteHook;
    }

    proc CheckInterp {slave} {
    if {![IsInterp $slave]} {
        return -code error \
            "\"$slave\" is not an interpreter managed by ::safe::"
    }
    }

    # Interface/entry point function and front end for "Configure"
    # This code is awfully pedestrian because it would need
    # more coupling and support between the way we store the
    # configuration values in safe::interp's and the Opt package
    # Obviously we would like an OptConfigure
    # to avoid duplicating all this code everywhere. -> TODO
    # (the app should share or access easily the program/value
    #  stored by opt)
    # This is even more complicated by the boolean flags with no values
    # that we had the bad idea to support for the sake of user simplicity
    # in create/init but which makes life hard in configure...
    # So this will be hopefully written and some integrated with opt1.0
    # (hopefully for tcl8.1 ?)
    proc interpConfigure {args} {
    switch [llength $args] {
        1 {
        # If we have exactly 1 argument
        # the semantic is to return all the current configuration
        # We still call OptKeyParse though we know that "slave"
        # is our given argument because it also checks
        # for the "-help" option.
        set Args [::tcl::OptKeyParse ::safe::interpIC $args]
        CheckInterp $slave
        set res {}
        lappend res [list -accessPath [Set [PathListName $slave]]]
        lappend res [list -statics    [Set [StaticsOkName $slave]]]
        lappend res [list -nested     [Set [NestedOkName $slave]]]
        lappend res [list -deleteHook [Set [DeleteHookName $slave]]]
        join $res
        }
        2 {
        # If we have exactly 2 arguments
        # the semantic is a "configure get"
        ::tcl::Lassign $args slave arg
        # get the flag sub program (we 'know' about Opt's internal
        # representation of data)
        set desc [lindex [::tcl::OptKeyGetDesc ::safe::interpIC] 2]
        set hits [::tcl::OptHits desc $arg]
                if {$hits > 1} {
                    return -code error [::tcl::OptAmbigous $desc $arg]
                } elseif {$hits == 0} {
                    return -code error [::tcl::OptFlagUsage $desc $arg]
                }
        CheckInterp $slave
        set item [::tcl::OptCurDesc $desc]
        set name [::tcl::OptName $item]
        switch -exact -- $name {
            -accessPath {
            return [list -accessPath [Set [PathListName $slave]]]
            }
            -statics {
            return [list -statics    [Set [StaticsOkName $slave]]]
            }
            -nested {
            return [list -nested     [Set [NestedOkName $slave]]]
            }
            -deleteHook {
            return [list -deleteHook [Set [DeleteHookName $slave]]]
            }
            -noStatics {
            # it is most probably a set in fact
            # but we would need then to jump to the set part
            # and it is not *sure* that it is a set action
            # that the user want, so force it to use the
            # unambigous -statics ?value? instead:
            return -code error\
                "ambigous query (get or set -noStatics ?)\
                use -statics instead"
            }
            -nestedLoadOk {
            return -code error\
                "ambigous query (get or set -nestedLoadOk ?)\
                use -nested instead"
            }
            default {
            return -code error "unknown flag $name (bug)"
            }
        }
        }
        default {
        # Otherwise we want to parse the arguments like init and create
        # did
        set Args [::tcl::OptKeyParse ::safe::interpIC $args]
        CheckInterp $slave
        # Get the current (and not the default) values of
        # whatever has not been given:
        if {![::tcl::OptProcArgGiven -accessPath]} {
            set doreset 1
            set accessPath [Set [PathListName $slave]]
        } else {
            set doreset 0
        }
        if {(![::tcl::OptProcArgGiven -statics]) \
            && (![::tcl::OptProcArgGiven -noStatics]) } {
            set statics    [Set [StaticsOkName $slave]]
        } else {
            set statics    [InterpStatics]
        }
        if {([::tcl::OptProcArgGiven -nested]) \
            || ([::tcl::OptProcArgGiven -nestedLoadOk]) } {
            set nested     [InterpNested]
        } else {
            set nested     [Set [NestedOkName $slave]]
        }
        if {![::tcl::OptProcArgGiven -deleteHook]} {
            set deleteHook [Set [DeleteHookName $slave]]
        }
        # we can now reconfigure :
        InterpSetConfig $slave $accessPath $statics $nested $deleteHook
        # auto_reset the slave (to completly synch the new access_path)
        if {$doreset} {
            if {[catch {::interp eval $slave {auto_reset}} msg]} {
            Log $slave "auto_reset failed: $msg"
            } else {
            Log $slave "successful auto_reset" NOTICE
            }
        }
        }
    }
    }


    ####
    #
    #  Functions that actually implements the exported APIs
    #
    ####


    #
    # safe::InterpCreate : doing the real job
    #
    # This procedure creates a safe slave and initializes it with the
    # safe base aliases.
    # NB: slave name must be simple alphanumeric string, no spaces,
    # no (), no {},...  {because the state array is stored as part of the name}
    #
    # Returns the slave name.
    #
    # Optional Arguments :
    # + slave name : if empty, generated name will be used
    # + access_path: path list controlling where load/source can occur,
    #                if empty: the master auto_path will be used.
    # + staticsok  : flag, if 0 :no static package can be loaded (load {} Xxx)
    #                      if 1 :static packages are ok.
    # + nestedok: flag, if 0 :no loading to sub-sub interps (load xx xx sub)
    #                      if 1 : multiple levels are ok.

    # use the full name and no indent so auto_mkIndex can find us
    proc ::safe::InterpCreate {
    slave
    access_path
    staticsok
    nestedok
    deletehook
    } {
    # Create the slave.
    if {[string compare "" $slave]} {
        ::interp create -safe $slave
    } else {
        # empty argument: generate slave name
        set slave [::interp create -safe]
    }
    Log $slave "Created" NOTICE

    # Initialize it. (returns slave name)
    InterpInit $slave $access_path $staticsok $nestedok $deletehook
    }


    #
    # InterpSetConfig (was setAccessPath) :
    #    Sets up slave virtual auto_path and corresponding structure
    #    within the master. Also sets the tcl_library in the slave
    #    to be the first directory in the path.
    #    Nb: If you change the path after the slave has been initialized
    #    you probably need to call "auto_reset" in the slave in order that it
    #    gets the right auto_index() array values.

    proc ::safe::InterpSetConfig {slave access_path staticsok\
        nestedok deletehook} {

    # determine and store the access path if empty
    if {[string equal "" $access_path]} {
        set access_path [uplevel #0 set auto_path]
        # Make sure that tcl_library is in auto_path
        # and at the first position (needed by setAccessPath)
        set where [lsearch -exact $access_path [info library]]
        if {$where == -1} {
        # not found, add it.
        set access_path [concat [list [info library]] $access_path]
        Log $slave "tcl_library was not in auto_path,\
            added it to slave's access_path" NOTICE
        } elseif {$where != 0} {
        # not first, move it first
        set access_path [concat [list [info library]]\
            [lreplace $access_path $where $where]]
        Log $slave "tcl_libray was not in first in auto_path,\
            moved it to front of slave's access_path" NOTICE

        }

        # Add 1st level sub dirs (will searched by auto loading from tcl
        # code in the slave using glob and thus fail, so we add them
        # here so by default it works the same).
        set access_path [AddSubDirs $access_path]
    }

    Log $slave "Setting accessPath=($access_path) staticsok=$staticsok\
        nestedok=$nestedok deletehook=($deletehook)" NOTICE

    # clear old autopath if it existed
    set nname [PathNumberName $slave]
    if {[Exists $nname]} {
        set n [Set $nname]
        for {set i 0} {$i<$n} {incr i} {
        Unset [PathToken $i $slave]
        }
    }

    # build new one
    set slave_auto_path {}
    set i 0
    foreach dir $access_path {
        Set [PathToken $i $slave] $dir
        lappend slave_auto_path "\$[PathToken $i]"
        incr i
    }
    Set $nname $i
    Set [PathListName $slave] $access_path
    Set [VirtualPathListName $slave] $slave_auto_path

    Set [StaticsOkName $slave] $staticsok
    Set [NestedOkName $slave] $nestedok
    Set [DeleteHookName $slave] $deletehook

    SyncAccessPath $slave
    }

    #
    #
    # FindInAccessPath:
    #    Search for a real directory and returns its virtual Id
    #    (including the "$")
proc ::safe::interpFindInAccessPath {slave path} {
    set access_path [GetAccessPath $slave]
    set where [lsearch -exact $access_path $path]
    if {$where == -1} {
        return -code error "$path not found in access path $access_path"
    }
    return "\$[PathToken $where]"
    }

    #
    # addToAccessPath:
    #    add (if needed) a real directory to access path
    #    and return its virtual token (including the "$").
proc ::safe::interpAddToAccessPath {slave path} {
    # first check if the directory is already in there
    if {![catch {interpFindInAccessPath $slave $path} res]} {
        return $res
    }
    # new one, add it:
    set nname [PathNumberName $slave]
    set n [Set $nname]
    Set [PathToken $n $slave] $path

    set token "\$[PathToken $n]"

    Lappend [VirtualPathListName $slave] $token
    Lappend [PathListName $slave] $path
    Set $nname [expr {$n+1}]

    SyncAccessPath $slave

    return $token
    }

    # This procedure applies the initializations to an already existing
    # interpreter. It is useful when you want to install the safe base
    # aliases into a preexisting safe interpreter.
    proc ::safe::InterpInit {
    slave
    access_path
    staticsok
    nestedok
    deletehook
    } {

    # Configure will generate an access_path when access_path is
    # empty.
    InterpSetConfig $slave $access_path $staticsok $nestedok $deletehook

    # These aliases let the slave load files to define new commands

    # NB we need to add [namespace current], aliases are always
    # absolute paths.
    ::interp alias $slave source {} [namespace current]::AliasSource $slave
    ::interp alias $slave load {} [namespace current]::AliasLoad $slave

    # This alias lets the slave use the encoding names, convertfrom,
    # convertto, and system, but not "encoding system <name>" to set
    # the system encoding.

    ::interp alias $slave encoding {} [namespace current]::AliasEncoding \
        $slave

    # This alias lets the slave have access to a subset of the 'file'
    # command functionality.

    AliasSubset $slave file file dir.* join root.* ext.* tail \
        path.* split

    # This alias interposes on the 'exit' command and cleanly terminates
    # the slave.

    ::interp alias $slave exit {} [namespace current]::interpDelete $slave

    # The allowed slave variables already have been set
    # by Tcl_MakeSafe(3)


    # Source init.tcl into the slave, to get auto_load and other
    # procedures defined:

    # We don't try to use the -rsrc on the mac because it would get
    # confusing if you would want to customize init.tcl
    # for a given set of safe slaves, on all the platforms
    # you just need to give a specific access_path and
    # the mac should be no exception. As there is no
    # obvious full "safe ressources" design nor implementation
    # for the mac, safe interps there will just don't
    # have that ability. (A specific app can still reenable
    # that using custom aliases if they want to).
    # It would also make the security analysis and the Safe Tcl security
    # model platform dependant and thus more error prone.

    if {[catch {::interp eval $slave\
        {source [file join $tcl_library init.tcl]}} msg]} {
        Log $slave "can't source init.tcl ($msg)"
        error "can't source init.tcl into slave $slave ($msg)"
    }

    return $slave
    }


    # Add (only if needed, avoid duplicates) 1 level of
    # sub directories to an existing path list.
    # Also removes non directories from the returned list.
    proc AddSubDirs {pathList} {
    set res {}
    foreach dir $pathList {
        if {[file isdirectory $dir]} {
        # check that we don't have it yet as a children
        # of a previous dir
        if {[lsearch -exact $res $dir]<0} {
            lappend res $dir
        }
        foreach sub [glob -nocomplain -- [file join $dir *]] {
            if {([file isdirectory $sub]) \
                && ([lsearch -exact $res $sub]<0) } {
            # new sub dir, add it !
                    lappend res $sub
                }
        }
        }
    }
    return $res
    }

    # This procedure deletes a safe slave managed by Safe Tcl and
    # cleans up associated state:

proc ::safe::interpDelete {slave} {

        Log $slave "About to delete" NOTICE

    # If the slave has a cleanup hook registered, call it.
    # check the existance because we might be called to delete an interp
    # which has not been registered with us at all
    set hookname [DeleteHookName $slave]
    if {[Exists $hookname]} {
        set hook [Set $hookname]
        if {![::tcl::Lempty $hook]} {
        # remove the hook now, otherwise if the hook
        # calls us somehow, we'll loop
        Unset $hookname
        if {[catch {eval $hook [list $slave]} err]} {
            Log $slave "Delete hook error ($err)"
        }
        }
    }

    # Discard the global array of state associated with the slave, and
    # delete the interpreter.

    set statename [InterpStateName $slave]
    if {[Exists $statename]} {
        Unset $statename
    }

    # if we have been called twice, the interp might have been deleted
    # already
    if {[::interp exists $slave]} {
        ::interp delete $slave
        Log $slave "Deleted" NOTICE
    }

    return
    }

    # Set (or get) the loging mecanism

proc ::safe::setLogCmd {args} {
    variable Log
    if {[llength $args] == 0} {
    return $Log
    } else {
    if {[llength $args] == 1} {
        set Log [lindex $args 0]
    } else {
        set Log $args
    }
    }
}

    # internal variable
    variable Log {}

    # ------------------- END OF PUBLIC METHODS ------------


    #
    # sets the slave auto_path to the master recorded value.
    # also sets tcl_library to the first token of the virtual path.
    #
    proc SyncAccessPath {slave} {
    set slave_auto_path [Set [VirtualPathListName $slave]]
    ::interp eval $slave [list set auto_path $slave_auto_path]
    Log $slave "auto_path in $slave has been set to $slave_auto_path"\
        NOTICE
    ::interp eval $slave [list set tcl_library [lindex $slave_auto_path 0]]
    }

    # base name for storing all the slave states
    # the array variable name for slave foo is thus "Sfoo"
    # and for sub slave {foo bar} "Sfoo bar" (spaces are handled
    # ok everywhere (or should))
    # We add the S prefix to avoid that a slave interp called "Log"
    # would smash our "Log" variable.
    proc InterpStateName {slave} {
    return "S$slave"
    }

    # Check that the given slave is "one of us"
    proc IsInterp {slave} {
    expr {[Exists [InterpStateName $slave]] && [::interp exists $slave]}
    }

    # returns the virtual token for directory number N
    # if the slave argument is given,
    # it will return the corresponding master global variable name
    proc PathToken {n {slave ""}} {
    if {[string compare "" $slave]} {
        return "[InterpStateName $slave](access_path,$n)"
    } else {
        # We need to have a ":" in the token string so
        # [file join] on the mac won't turn it into a relative
        # path.
        return "p(:$n:)"
    }
    }
    # returns the variable name of the complete path list
    proc PathListName {slave} {
    return "[InterpStateName $slave](access_path)"
    }
    # returns the variable name of the complete path list
    proc VirtualPathListName {slave} {
    return "[InterpStateName $slave](access_path_slave)"
    }
    # returns the variable name of the number of items
    proc PathNumberName {slave} {
    return "[InterpStateName $slave](access_path,n)"
    }
    # returns the staticsok flag var name
    proc StaticsOkName {slave} {
    return "[InterpStateName $slave](staticsok)"
    }
    # returns the nestedok flag var name
    proc NestedOkName {slave} {
    return "[InterpStateName $slave](nestedok)"
    }
    # Run some code at the namespace toplevel
    proc Toplevel {args} {
    namespace eval [namespace current] $args
    }
    # set/get values
    proc Set {args} {
    eval Toplevel set $args
    }
    # lappend on toplevel vars
    proc Lappend {args} {
    eval Toplevel lappend $args
    }
    # unset a var/token (currently just an global level eval)
    proc Unset {args} {
    eval Toplevel unset $args
    }
    # test existance
    proc Exists {varname} {
    Toplevel info exists $varname
    }
    # short cut for access path getting
    proc GetAccessPath {slave} {
    Set [PathListName $slave]
    }
    # short cut for statics ok flag getting
    proc StaticsOk {slave} {
    Set [StaticsOkName $slave]
    }
    # short cut for getting the multiples interps sub loading ok flag
    proc NestedOk {slave} {
    Set [NestedOkName $slave]
    }
    # interp deletion storing hook name
    proc DeleteHookName {slave} {
    return [InterpStateName $slave](cleanupHook)
    }

    #
    # translate virtual path into real path
    #
    proc TranslatePath {slave path} {
    # somehow strip the namespaces 'functionality' out (the danger
    # is that we would strip valid macintosh "../" queries... :
    if {[regexp {(::)|(\.\.)} $path]} {
        error "invalid characters in path $path"
    }
    set n [expr {[Set [PathNumberName $slave]]-1}]
    for {} {$n>=0} {incr n -1} {
        # fill the token virtual names with their real value
        set [PathToken $n] [Set [PathToken $n $slave]]
    }
    # replaces the token by their value
    subst -nobackslashes -nocommands $path
    }


    # Log eventually log an error
    # to enable error logging, set Log to {puts stderr} for instance
    proc Log {slave msg {type ERROR}} {
    variable Log
    if {[info exists Log] && [llength $Log]} {
        eval $Log [list "$type for slave $slave : $msg"]
    }
    }


    # file name control (limit access to files/ressources that should be
    # a valid tcl source file)
    proc CheckFileName {slave file} {
    # limit what can be sourced to .tcl
    # and forbid files with more than 1 dot and
    # longer than 14 chars
    set ftail [file tail $file]
    if {[string length $ftail]>14} {
        error "$ftail: filename too long"
    }
    if {[regexp {\..*\.} $ftail]} {
        error "$ftail: more than one dot is forbidden"
    }
    if {[string compare $ftail "tclIndex"] && \
        [string compare -nocase [file extension $ftail]    ".tcl"]} {
        error "$ftail: must be a *.tcl or tclIndex"
    }

    if {![file exists $file]} {
        # don't tell the file path
        error "no such file or directory"
    }

    if {![file readable $file]} {
        # don't tell the file path
        error "not readable"
    }
    }


    # AliasSource is the target of the "source" alias in safe interpreters.

    proc AliasSource {slave args} {

    set argc [llength $args]
    # Allow only "source filename"
    # (and not mac specific -rsrc for instance - see comment in ::init
    # for current rationale)
    if {$argc != 1} {
        set msg "wrong # args: should be \"source fileName\""
        Log $slave "$msg ($args)"
        return -code error $msg
    }
    set file [lindex $args 0]

    # get the real path from the virtual one.
    if {[catch {set file [TranslatePath $slave $file]} msg]} {
        Log $slave $msg
        return -code error "permission denied"
    }

    # check that the path is in the access path of that slave
    if {[catch {FileInAccessPath $slave $file} msg]} {
        Log $slave $msg
        return -code error "permission denied"
    }

    # do the checks on the filename :
    if {[catch {CheckFileName $slave $file} msg]} {
        Log $slave "$file:$msg"
        return -code error $msg
    }

    # passed all the tests , lets source it:
    if {[catch {::interp invokehidden $slave source $file} msg]} {
        Log $slave $msg
        return -code error "script error"
    }
    return $msg
    }

    # AliasLoad is the target of the "load" alias in safe interpreters.

    proc AliasLoad {slave file args} {

    set argc [llength $args]
    if {$argc > 2} {
        set msg "load error: too many arguments"
        Log $slave "$msg ($argc) {$file $args}"
        return -code error $msg
    }

    # package name (can be empty if file is not).
    set package [lindex $args 0]

    # Determine where to load. load use a relative interp path
    # and {} means self, so we can directly and safely use passed arg.
    set target [lindex $args 1]
    if {[string length $target]} {
        # we will try to load into a sub sub interp
        # check that we want to authorize that.
        if {![NestedOk $slave]} {
        Log $slave "loading to a sub interp (nestedok)\
            disabled (trying to load $package to $target)"
        return -code error "permission denied (nested load)"
        }

    }

    # Determine what kind of load is requested
    if {[string length $file] == 0} {
        # static package loading
        if {[string length $package] == 0} {
        set msg "load error: empty filename and no package name"
        Log $slave $msg
        return -code error $msg
        }
        if {![StaticsOk $slave]} {
        Log $slave "static packages loading disabled\
            (trying to load $package to $target)"
        return -code error "permission denied (static package)"
        }
    } else {
        # file loading

        # get the real path from the virtual one.
        if {[catch {set file [TranslatePath $slave $file]} msg]} {
        Log $slave $msg
        return -code error "permission denied"
        }

        # check the translated path
        if {[catch {FileInAccessPath $slave $file} msg]} {
        Log $slave $msg
        return -code error "permission denied (path)"
        }
    }

    if {[catch {::interp invokehidden\
        $slave load $file $package $target} msg]} {
        Log $slave $msg
        return -code error $msg
    }

    return $msg
    }

    # FileInAccessPath raises an error if the file is not found in
    # the list of directories contained in the (master side recorded) slave's
    # access path.

    # the security here relies on "file dirname" answering the proper
    # result.... needs checking ?
    proc FileInAccessPath {slave file} {

    set access_path [GetAccessPath $slave]

    if {[file isdirectory $file]} {
        error "\"$file\": is a directory"
    }
    set parent [file dirname $file]
    if {[lsearch -exact $access_path $parent] == -1} {
        error "\"$file\": not in access_path"
    }
    }

    # This procedure enables access from a safe interpreter to only a subset of
    # the subcommands of a command:

    proc Subset {slave command okpat args} {
    set subcommand [lindex $args 0]
    if {[regexp $okpat $subcommand]} {
        return [eval {$command $subcommand} [lrange $args 1 end]]
    }
    set msg "not allowed to invoke subcommand $subcommand of $command"
    Log $slave $msg
    error $msg
    }

    # This procedure installs an alias in a slave that invokes "safesubset"
    # in the master to execute allowed subcommands. It precomputes the pattern
    # of allowed subcommands; you can use wildcards in the pattern if you wish
    # to allow subcommand abbreviation.
    #
    # Syntax is: AliasSubset slave alias target subcommand1 subcommand2...

    proc AliasSubset {slave alias target args} {
    set pat ^(; set sep ""
    foreach sub $args {
        append pat $sep$sub
        set sep |
    }
    append pat )\$
    ::interp alias $slave $alias {}\
        [namespace current]::Subset $slave $target $pat
    }

    # AliasEncoding is the target of the "encoding" alias in safe interpreters.

    proc AliasEncoding {slave args} {

    set argc [llength $args]

    set okpat "^(name.*|convert.*)\$"
    set subcommand [lindex $args 0]

    if {[regexp $okpat $subcommand]} {
        return [eval ::interp invokehidden $slave encoding $subcommand \
            [lrange $args 1 end]]
    }

    if {[string match $subcommand system]} {
        if {$argc == 1} {
        # passed all the tests , lets source it:
        if {[catch {::interp invokehidden \
            $slave encoding system} msg]} {
            Log $slave $msg
            return -code error "script error"
        }
        } else {
        set msg "wrong # args: should be \"encoding system\""
        Log $slave $msg
        error $msg
        }
    } else {
        set msg "wrong # args: should be \"encoding option ?arg ...?\""
        Log $slave $msg
        error $msg
    }

    return $msg
    }

}